The foreach statement of the C# language (for each in Visual Basic) returns an object of the type of the elements in the collection. Since each element of the DictionaryBase is a key/value pair, the element type is not the type of the key or the type of the value. Instead, the element type is DictionaryEntry.

The foreach statement is a wrapper around the enumerator, which only allows reading from, not writing to, the collection.

Note

Because keys can be inherited and their behavior changed, their absolute uniqueness cannot be guaranteed by comparisons using the Equals method.

Notes to Implementers:

This base class is provided to make it easier for implementers to create a strongly typed custom collection. Implementers are encouraged to extend this base class instead of creating their own.

Members of this base class are protected and are intended to be used through a derived class only.

Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

This implementation does not provide a synchronized (thread-safe) wrapper for a DictionaryBase, but derived classes can create their own synchronized versions of the DictionaryBase using the SyncRoot property.

Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.